1. Field of the Invention
The present invention relates to a golf ball superior in shot feeling, impact resilience, controllability and scuff resistance as a whole.
2. Description of the Background Art
As a resin component of a cover material for two-piece golf balls and thread-wound golf balls, an ionomer resin of an ethylene-(meth)acrylic acid copolymer has widely been employed because of its superior durability with respect to shot and cut resistance. However, the ionomer resin provides “hard feel” when being shot as compared with balata rubber having been used for cover materials, and the ionomer resin has a higher hardness than balata rubber. Therefore, it is difficult to apply a spin to a ball covered with the ionomer resin and thus the ionomer resin is inferior in controllability.
Balata covered golf balls have widely been used typically by skilled and professional golfers because of its excellent shot feeling and controllability. However, such balata covered golf balls are produced through a complicated manufacturing process and have an inferior cut resistance. Then, various soft covers are proposed these days as a substitute for the balata cover.
For example, U.S. Pat. No. 4,884,814 discloses a technique of using a soft ionomer resin as a base resin for a cover. Specifically, an ethylene-(meth)acrylic acid-(meth)acrylic acid ester terpolymer, which is a relatively flexible ionomer resin, is blended, at a certain ratio, with an ionomer resin of an ethylene-(meth)acrylic acid copolymer in a certain range of physical properties, and the blended ionomers are used to form a soft/hard ionomer-blended cover. This technique overcomes the disadvantages with respect to shot feeling and controllability of conventional golf balls having covers of an ionomer resin of an ethylene-(meth)acrylic acid copolymer.
The soft/hard ionomer-blended cover of the above technique is made softer and thus a spin is readily applied to a golf ball with this cover in an iron shot, while friction increases between a club face and the cover. When a golf ball like a two-piece solid golf ball having a hard core material is shot, the surface of the cover is chipped off by grooves of an iron club so that the surface of the ball is burred. The lower hardness of the ionomer cover reduces the impact resilience of the cover itself, resulting in deterioration in impact resilience of the ball.
In GB 2264302, it is proposed, for the purpose of improving resistance to abrasion of the ionomer cover caused by shot by the iron club, to use, as a cover, at least two types of materials made from metal salt of ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester terpolymer having low flexural modulus. However, this technique is insufficient with respect to scuff resistance when the golf ball is struck with the iron club as described above and has a deteriorated impact resilience.
Japanese Patent Laying-Open No. 10-179802 proposes a golf ball having a base resin material for a cover structured to have as a main component a heated mixture of two components, that is, an ionomer resin and a styrene-butadiene-styrene block copolymer containing an epoxy group or a styrene-isoprene-styrene block copolymer containing an epoxy group. A cover composition constituting the cover has a flexural modulus of 50 to 300 MPa and a shore D hardness of 40 to 60.
Further, GB 2311530 proposes a golf ball having a base resin material for a cover that has as a main component a heated mixture of three components, that is, ionomer resin, acid-modified thermoplastic elastomer or thermoplastic elastomer having an OH group at the end of the polymer chain, and a styrene-butadiene-styrene block copolymer containing an epoxy group or a styrene-isoprene-styrene block copolymer containing an epoxy group. A cover composition constituting the cover has a flexural modulus of 50 to 300 MPa and a shore D hardness of 40 to 60.
These techniques achieve improvement in shot feeling, controllability and cut resistance, however, they are unsatisfactory in terms of impact resilience.